1. Field of the Invention
The present invention relates to an electron emitting device, an electron source, an image forming apparatus, and methods for producing them. More particularly, the invention concerns the electron emitting device with organic films thereon and, the electron source, image forming apparatus, and producing methods of them.
2. Related Background Art
The electron emitting devices conventionally known are generally classified under two types using thermionic emission elements and cold cathode emission elements. The cold cathode emission elements include the field emission (FE) type, the metal/insulator/metal (MIM) type, the surface conduction type electron emitting devices, and so on.
In some of these electron emitting devices a film of carbon or the like is laid on the device surface for the purpose of improving electron emission characteristics thereof.
For example, EP-A-660357, Japanese Patent Application Laid-Open No. 07-235255, Japanese Patent Application Laid-Open No. 08-007749, etc. describe producing methods of the electron emitting device comprising an energization forming operation of forming an electrically conductive film between device electrodes and applying voltage between the device electrodes so as to form an electron emitting region in the conductive, thin film and an activation operation, carried out thereafter, of again applying voltage between the device electrodes in an atmosphere containing a carbon compound in order to increase electron emission efficiency.
Further, Japanese Patent Application Laid-Open No. 9-237571 and EP-A-788130 describe producing methods of the electron emitting device having a step of forming films of an organic substance on the conductive film formed between the device electrodes, by applying a thermosetting resin, an electron-beam negative resist, or an organic material such as polyacrylonitrile or the like thereonto by a spin coat method and a step of carbonizing these organic substance films in order to increase the electron emission efficiency as was the case in the above.
In the producing methods described in above Japanese Patent Application Laid-Open No. 9-237571 and EP-A-788130, instability of the electron emitting device characteristics during driving is overcome by adopting a step of eliminating the organic substance films remaining on the conductive film under a reactive gas atmosphere after the above carbonization step. This suggests that in the above conventional technology the existence of the organic substance films on the conductive film forming the electron emitting device affects the electron emission characteristics during driving, and only one solution to it was the removal of the organic substance films.
An object of the present invention is to provide an electron emitting device in which the influence of the organic films laid on the electron emitting device, upon the electron emission characteristics is reduced to the utmost, and a producing method thereof.
Another object of the present invention is to provide an electron emitting device with higher electron emission efficiency, and a producing method thereof.
The present invention involves structures described below, especially.
Namely, the present invention is an electron emitting device comprising, on a substrate, a pair of electrically conductive films spaced with a gap in between, and an organic film laid on said conductive films, wherein said organic film is placed in an area on said conductive films.
The present invention is also an electron emitting device comprising, on a substrate, a pair of electrically conductive films spaced with a gap in between, and an organic film laid on said conductive films, wherein an overhang portion of said organic film from edges of said conductive films on said substrate is not more than 5 xcexcm.
The present invention is also an electron emitting device comprising, on a substrate, a pair of conductive films spaced with a gap in between, an organic film laid on said conductive films, and carbon films laid on ends of said pair of conductive films facing the gap, wherein said organic film is placed in an area on said conductive films.
The present invention is also an electron emitting device comprising, on a substrate, a pair of conductive films spaced with a gap in between, an organic film laid on said conductive films, and. carbon films laid on ends of said pair of conductive films facing the gap, wherein an overhang portion of said organic film from edges of said conductive films on said substrate is not more than 5 xcexcm.
The present invention is also the invention of the electron emitting devices further involving the following configurations, in addition to the above configurations. Namely,
said organic film is a film comprised of an organic polymer.
Further, said organic polymer is a heat-resistant organic polymer, or polyimide.
The present invention is also an electron source comprising a plurality of electron emitting devices, wherein said electron emitting devices are those described above.
The present invention is also an image forming apparatus comprising an electron source having a plurality of electron emitting devices, and an image forming member for forming an image under irradiation of electrons emitted from the electron source, wherein said electron emitting devices are those described above.
The present invention is also a method for producing an electron emitting device, the producing method comprising a step of forming an electrically conductive film on a substrate, a step of forming an organic film on said conductive film, and a step of energizing the conductive film with said organic film formed thereon, wherein said step of forming the organic film comprises a step of delivering a liquid comprising a material for forming said organic film, into an area on said conductive film by an ink jet method.
The present invention is also a method for producing an electron emitting device, the producing method comprising a step of forming an electrically conductive film on a substrate, a step of forming an organic film on said conductive film, and a step of energizing the conductive film with said organic film formed thereon, wherein said step of forming the organic film comprises a step of delivering a liquid comprising a material for forming said organic film, onto said conductive film by an ink jet method, and wherein said organic film is formed so that an overhang portion of the organic film from an edge of said conductive film on the substrate is not more than 5 xcexcm.
The present invention is also a method for producing an electron emitting device, the producing method comprising a step of forming an electrically conductive film on a substrate, a step of forming an organic film on said conductive film, and a step of energizing the conductive film with said organic film formed thereon, wherein said step of forming the organic film comprises a step of delivering a liquid comprising a material for forming said organic film, onto said conductive film by an ink jet method, said producing method further comprising a step of making a difference in wettability against said liquid between a surface of said conductive film and a surface of said substrate, prior to said step of forming the organic film.
The present invention is also a method for producing an electron emitting device, the producing method comprising a step of forming an electrically conductive film on a substrate, a step of forming an organic film on said conductive film, and a step of energizing the conductive film with said organic film formed thereon, wherein said step of forming the organic film comprises a step of delivering a liquid comprising a material for forming said organic film, onto said conductive film by an ink jet method, said producing method further comprising a step of subjecting said substrate to a surface treatment for decreasing wettability of a surface of the substrate against said liquid, prior to said step of forming the organic film.
The present invention is also the invention of the producing methods of the electron emitting device further involving the following configurations, in addition to the above configurations. Namely,
said liquid is a liquid containing polyamic acid, an amine, and an organic solvent.
Further, said amine is at least one selected from diethanolamine, triethanolamine, and trishydroxymethylaminomethane.
Said ink jet method is a method of generating a bubble in the liquid by making use of thermal energy to discharge the liquid, or a method of discharging the liquid by making use of mechanical energy.
The present invention is also a method for producing an electron source comprising a plurality of electron emitting devices, wherein said electron emitting devices are produced by the method described above.
The present invention is also a method for producing an image forming apparatus comprising an electron source having a plurality of electron emitting devices, and an image forming member for forming an image under irradiation of electrons emitted from the electron source, wherein said electron emitting devices are produced by the method described above.
The present invention described above has been accomplished based on acquisition of the following knowledge; the instability of the electron emission characteristics during driving of the electron emitting device with the organic film is caused by decrease in the electron emission efficiency resulting from the fact that the organic film of the electron emitting device becomes conductive during the producing step thereof or during driving, this results in creating leak paths of current in the gap part of the conductive films, and ohmic current flows in addition to the current related to the electron emission current.
Namely, in the case of the electron emitting device of the present invention, since the organic films formed for protection of the surface of the conductive films, or the organic films remaining as a result of the formation of the carbon films during the producing step, are placed in areas on the conductive films, this structure can prevent the creation of the leak paths in the above gap due to the change of the organic films on the substrate into conductive films in the case wherein the organic films also exist on the substrate surface outside the areas of the conductive films.
In the case of the electron emitting device of the present invention, even if the above organic films also exist on the substrate surface outside the areas of the conductive films, since the degree thereof is decreased to 5 xcexcm or less, this can prevent the creation of such leak paths in the above gap as to considerably degrade the electron emission characteristics.
Here the above term xe2x80x9c5 xcexcm or lessxe2x80x9d means, as illustrated in FIG. 6C described hereinafter, that a maximum overhang portion D of the above organic films 41 from an edge of the above conductive films 4 on the substrate 1 is not more than 5 xcexcm.
According to the producing method of the electron emitting device of the present invention, the formation of the above organic films comprises the step of delivering the liquid containing the material for formation of the organic films into areas on the conductive films by the ink jet method, whereby the organic films can be formed in the areas on the conductive films, as described above, thereby preventing the creation of leak paths in the above gap.
The method of delivering the above liquid into the areas on the above conductive films by the ink jet method became possible, for example, by controlling the composition of the above liquid, as described hereinafter.
According to the producing method of the electron emitting device of the present invention, the formation of the above organic films is carried out after the difference in wettability against the liquid delivered is made between the surface of the above conductive films and the surface of the above substrate in delivering the above liquid onto the conductive films by the ink jet method, preferably, after the above substrate is subjected to the surface treatment to decrease the wettability of the substrate surface against the above liquid, whereby the organic films are formed within the areas on the above conductive films, or, even if the organic films are also formed on the substrate surface outside the areas of the conductive films, the degree thereof is 5 xcexcm or less as stated above, thereby preventing the creation of leak paths in the above gap.
As described above, according to the electron emitting device of the present invention and the producing method thereof, it is extremely rare, especially, for part of the organic films of the device to become conductive during the producing step or during driving so as to allow flow of the ohmic current in addition to the current related to the electron emission current, thereby decreasing the electron emission efficiency, and thus the good device is obtained.